These five projects deal with the cytology and physiology of the retina. They are directed at studying cell structure and function and the special and vegetative metabolism of different cell types, as they may relate to the processing of visual information. Some also deal with retinal disease, particularly that based on genetic lesions involving photoreceptors. For studying the kinetics of light-induced changes in nucleotides and cyclic nucleotides of photoreceptor outer segments, one project uses frozen outer segments shaved from frog retinas subjected to ultrarapid freezing at a known, very brief interval after a light flash. Another project uses mutant mouse retinas with some residual light sensitivity despite the absence of photoreceptor outer segments and most receptors, and seeks to describe the properties of a residual light-influenced biochemistry and locate the molecules involved. Using identified layers obtained from rabbit retinas frozen after suprafusion with physiological salines containing pharmacological agents, a third project seeks to identify the layers on which these agents act. A fourth project uses incubated mouse retinas to clarify a selective effect of the indoleamine, 5-methoxytryptamine on a dark cyclic AMP metabolism. The last project is purely cytological, seeking by electron microscopy to describe two different tiers of probable gap junctions involving primate photoreceptors.